Master Flatfield

This module provides algorithms to compute a master flatfield. Several methods are available to deal with different flatfield characteristics. More...

Functions
hdrl_parameter *	hdrl_flat_parameter_create (cpl_size filter_size_x, cpl_size filter_size_y, hdrl_flat_method method)
	Creates FLAT Parameters object.
cpl_boolean	hdrl_flat_parameter_check (const hdrl_parameter *self)
	Check that the parameter is a FLAT parameter.
cpl_size	hdrl_flat_parameter_get_filter_size_x (const hdrl_parameter *p)
	Access the filter_size_x in the FLAT parameter.
cpl_size	hdrl_flat_parameter_get_filter_size_y (const hdrl_parameter *p)
	Access the filter_size_y in the FLAT parameter.
hdrl_flat_method	hdrl_flat_parameter_get_method (const hdrl_parameter *p)
	Access the method in the FLAT parameter.
cpl_parameterlist *	hdrl_flat_parameter_create_parlist (const char *base_context, const char *prefix, const hdrl_parameter *defaults)
	Create a parameter list for the FLAT computation.
hdrl_parameter *	hdrl_flat_parameter_parse_parlist (const cpl_parameterlist *parlist, const char *prefix)
	Parse a parameterlist to create input parameters for the FLAT.
cpl_error_code	hdrl_flat_compute (hdrl_imagelist *hdrl_data, const cpl_mask *stat_mask, const hdrl_parameter *collapse_params, hdrl_parameter *flat_params, hdrl_image **master, cpl_image **contrib_map)
	compute high or low frequency master flat with median filtering

Detailed Description

This module provides algorithms to compute a master flatfield. Several methods are available to deal with different flatfield characteristics.

The routines in this module can be used to derive a high frequency or a low frequency master flatfield.

HIGH frequency algorithm:

The algorithm first smoothes the input images by a median filter and divides each input image through the smoothed image. The smoothed images is considered to be noiseless i.e. the relative error of the resulting images is the same as the one of the input image. Then all residual images are collapsed into a single master flatfield. The collapsing can be done with all methods currently implemented in hdrl. Moreover, it is also possible to give a static mask to the algorithm which e.g. allows the user to distinguish illuminated and not illuminated regions. In this case the smoothing procedure is done twice, once for the illuminated region and once for the blanked region. This ensures that the information of one region does not influence the other regions during the smoothing process.

LOW frequency algorithm:

The algorithm multiplicatively normalizes the input images by the median of the image to unity. A static mask can be provided to the algorithm in order to define the pixels that should be taken into account when computing the normalisation factor. This allows the user to normalize the flatfield e.g. only by the illuminated section. Then all normalized images are collapsed into a single master flatfield. The collapsing can be done with all methods currently implemented in hdrl. Finally, the master flatfield is smoothed by a median filter. The associated error of the final masterframe is the error derived via error propagation of the previous steps, i.e. the smoothing itself is considered noiseless.

The calculation is performed by calling the top-level function hdrl_flat_compute() and the parameters passed to this function can be created by calling hdrl_flat_parameter_create(). Additional one has to pass also the collapse parameter created e.g. via hdrl_collapse_mean_parameter_create(), ... Note that the function will overwrite the input imagelist in order to conserve memory. Its contents after the call are undefined and it must be deleted by the caller.

Function Documentation

hdrl_flat_compute()

cpl_error_code hdrl_flat_compute	(	hdrl_imagelist *	hdrl_data,
		const cpl_mask *	stat_mask,
		const hdrl_parameter *	collapse_params,
		hdrl_parameter *	flat_params,
		hdrl_image **	master,
		cpl_image **	contrib_map
	)

compute high or low frequency master flat with median filtering

Parameters

hdrl_data	input flats, will be overwritten!
stat_mask	input mask to select the regions for statistics or smoothing
collapse_params	parameter controlling the collapse algorithm
flat_params	parameter controlling the flatfield algorithm
master	returned masterflat
contrib_map	returned contribution map

The algorithms are described in the master flatfield module documentation

Note

the function will overwrite the input imagelist in order to conserve memory. Its contents after the call are undefined and it must be deleted by the caller.

hdrl_flat_parameter_check()

cpl_boolean hdrl_flat_parameter_check

(

const hdrl_parameter *

self

)

Check that the parameter is a FLAT parameter.

Parameters

self	The parameter to check

Returns

True or False

hdrl_flat_parameter_create()

hdrl_parameter * hdrl_flat_parameter_create	(	cpl_size	filter_size_x,
		cpl_size	filter_size_y,
		hdrl_flat_method	method
	)

Creates FLAT Parameters object.

PRIVATE

Parameters

filter_size_x	Smoothing filter size in x-direction
filter_size_y	Smoothing filter size in y-direction
method	used method

Returns

The FLAT parameters object.

      It needs to be deallocated with hdrl_parameter_delete()

See also

hdrl_parameter_delete()

hdrl_flat_compute()

hdrl_flat_parameter_create_parlist()

cpl_parameterlist * hdrl_flat_parameter_create_parlist	(	const char *	base_context,
		const char *	prefix,
		const hdrl_parameter *	defaults
	)

Create a parameter list for the FLAT computation.

Parameters

base_context	base context of parameter (e.g. recipe name)
prefix	prefix of parameter, may be empty string
defaults	default values

Creates a parameterlist with the FLAT parameters:

• base_context.prefix.filter_size_x
• base_context.prefix.filter_size_y
• base_context.prefix.method The CLI aliases omit the base_context.

hdrl_flat_parameter_get_filter_size_x()

cpl_size hdrl_flat_parameter_get_filter_size_x

(

const hdrl_parameter *

p

)

Access the filter_size_x in the FLAT parameter.

Parameters

p	The FLAT parameter

Returns

The filter_size_x

hdrl_flat_parameter_get_filter_size_y()

cpl_size hdrl_flat_parameter_get_filter_size_y

(

const hdrl_parameter *

p

)

Access the filter_size_y in the FLAT parameter.

Parameters

p	The FLAT parameter

Returns

The filter_size_y

hdrl_flat_parameter_get_method()

hdrl_flat_method hdrl_flat_parameter_get_method

(

const hdrl_parameter *

p

)

Access the method in the FLAT parameter.

Parameters

p	The FLAT parameter

Returns

The method

hdrl_flat_parameter_parse_parlist()

hdrl_parameter * hdrl_flat_parameter_parse_parlist	(	const cpl_parameterlist *	parlist,
		const char *	prefix
	)

Parse a parameterlist to create input parameters for the FLAT.

Parameters

parlist	parameter list to parse
prefix	prefix of parameter name

Returns

Input parameters for the FLAT computation

Reads a parameterlist in order to create FLAT image parameters. Expects a parameterlist containing:

• prefix.filter_size_x
• prefix.filter_size_y
• prefix.method